There has been speculation recently that the rate of lung cancer may be increasing among nonsmokers. Two subsequent studies suggested that passive inhalation of a spouse's cigarette smoke may double a nonsmoker's risk of getting lung cancer. In addition, there is some evidence that lung cancer risks from certain occupations are higher among nonsmokers than among smokers. We want to know what fraction, if any, of lung cancers among nonsmokers can be explained by passive smoking and occupation, and whether other risk factors could be identified which are responsible for a significant proportion of lung cancer cases among nonsmokers. We propose a population-based case-control epidemiologic study comparing 450 lung cancer patients who have never smoked with 450 matched nonsmoking controls. Personal interviews will be used to collect data on passive smoking, history of occupational exposures, environmental exposures, dietary Vitamin A and Beta-carotene, history of obstructive lung disease, and family history of lung cancer. Using a pathologic and clinical review of the 450 nonsmoking lung cancer cases matched to an additional 450 smoking lung cancer cases, we will compare the two groups with respect to duration and type of symptoms, operability, survival, location of tumors and histologic type. The proposed study has potential applications not only in the prevention, diagnosis and treatment of lung cancer among nonsmokers, but also in discovering risk factors for lung cancer in general. It may be able to detect factors which are overshadowed in other studies by the strong influence of smoking on lung cancer risk.